Technical Field
The present invention relates to an alumina/NiO/ZnO and an alumina/ZnO composite, a method in which the composites are obtained, and a method in which the composites are used as adsorbents in a method of desulfurization of diesel fuel.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The demand for transportation fuels has been increasing in most countries for the past two decades, and the diesel fuel demand is expected to increase significantly in the future (Brady, A. “Global Refining Margins Look Poor in Short Term, Buoyant Later Next Decade,” Oil Gas J., 1999, 97 (46), 75-80—incorporated herein by reference in its entirety). Crude oil, a complex mixture of organic liquids, is considered the largest source of energy and the major portions of the crude oils are used as transportation. Hetero atoms include sulfur (0-5%), nitrogen (0-0.2%), and other elements (e.g. oxygen, nickel, vanadium and iron) ranging from 0 to 0.1% weight and the sulfur content is expressed as a percentage of sulfur by weight based on the total weight of the crude oil and varies from less than 0.1% to greater than 5% depending on the type and source of crude oils (Gary, J. H., and Hand werk, G. E., “Petroleum Refining, Technology and Economics, Second Edition,” Marcel Dekker, New York, 1998—incorporated herein by reference in its entirety).
It is known that, sulfur compounds present in fuels lead to the emission of sulfur oxide gases (SOx). These gases react with water in the atmosphere to form sulfates and acid rain which damages buildings, destroys automotive paint finishes, acidifies soil, and ultimately leads to loss of forests and various other ecosystems (W. L. Fang, Inventory of U. S. “Greenhouse Gas Emissions and Sinks, 1990-2003,” Clean Air Markets Division, 2004—incorporated herein by reference in its entirety). Even traces of sulfur compounds present in diesel fuels poisons the oxidative catalyst used in the emission control system and reduces their effectiveness for the oxidation of harmful carbon monoxide, hydrocarbons and volatile organic matter. Sulfur emissions also cause severe human health such as, respiratory illnesses, aggravate heart disease, trigger asthma, and contribute to formation of atmospheric particulates (Vimal Chandra Srivastava, “An evaluation of desulfurization technologies for sulfur removal from liquid Fuels,” RSC Advances, 2012, 2, 759-783—incorporated herein by reference in its entirety), global warming and water pollution (Venner SF, “EU environmental laws impact fuels' requirements,” Hydrocarb Process 2000; 79:51-7—incorporated herein by reference in its entirety). Environmental regulations have been introduced in many countries around the world to reduce the sulfur content in diesel fuel to ultra low levels of 10 ppm (US EPA, Diesel Fuel Quality: Advance Notice of Proposed Rulemaking, EPA420-F-99-011, Office of Mobile Sources, May 1999—incorporated herein by reference in its entirety).
In an attempt to achieve sulfur levels less than 10 ppm, there are several emerging trends towards minimizing sulfur content in transportation fuels. In comparison to various desulfurization techniques, adsorption is considered to be an efficient and economical way for removing organosulfur compounds due to its low-energy consumption, and works at ambient conditions. Adsorption is the most common hydrodesulphurization (HDS) alternative method currently used to achieve ultra-clean fuels (Tymchyshyn M., “Deep Desulphurization of Diesel Fuels,” Lakehead University, April (2008)—incorporated herein by reference in its entirety).
A variety of adsorbents such as ion-exchanged zeolites, supported metals, metal oxides, activated carbons, alumina, ionic liquids (C. S. Song, “An overview of new approaches to deep desulfurization for ultra-clean gasoline, diesel fuel and jet fuel,” Catal. Today, 86 (2003) 211-263; Y. S. Shen, et al., “Selective adsorption for removing sulfur: a potential ultra-deep desulfurization approach of jet fuels,” RSC Adv., 2 (2012) 1700-1711—each incorporated herein by reference in its entirety) and other commercial adsorbents have been reported for the adsorptive desulfurization under ambient conditions. Activated alumina has a good adsorptive properties for the removal of organic compound from aqueous solutions (A. K. Bajpai, et al., “Studies on the adsorption of sulfapyridine at the solution-alumina interface, J. Colloid Interface Sci. 187 (1997) 96-104—each incorporated herein by reference in its entirety). Srivastava et al. (A. Srivastav, V. C. Srivastava, Adsorptive desulfurization by activated alumina Journal of Hazardous Materials 170 (2009) 1133-1140—incorporated herein by reference in its entirety) investigated the removal of DBT dissolved in n-hexane by commercial grade activated alumina (aluminum oxide) as adsorbent. Kim et al. (J. H. Kim, et al., “Ultra-deep desulfurization and denitrogenation of diesel fuel by selective adsorption over three different adsorbents: a study on adsorptive selectivity and mechanism,” Catal. Today 111 (2006) 74-83—incorporated herein by reference in its entirety) studied the adsorptive desulfurization using a model diesel fuel over three typical adsorbents (activated carbon, activated alumina and nickel-based adsorbent) in a fixed-bed adsorption system.
To improve adsorption capacity of alumina for removing sulfur-containing compounds in fuels, the surface chemistry, as well as the pore structure of activated alumina, can be modified (Jeevanandam P, et al., “Adsorption of thiophenes out of hydrocarbons using metal impregnated nanocrystalline aluminum oxide.,” Micropor Mesopor Mater 2005:101-10—incorporated herein by reference in its entirety). Recently, Wang et al. (J. Wang, et al., “Alumina-supported manganese oxide sorbent prepared by sub-critical water impregnation for hot coal gas desulfurization,” Fuel Processing Technology (2013)—incorporated herein by reference in its entirety) investigated the removal of H2S from hot coal gas by Alumina-supported manganese oxide sorbents. It is reported that Nickel has an affinity to the organic sulfur compounds and it is the active sites on Ni/ZnO for desulfurization process, where the organic sulfur compounds in the diesel are decomposed on the surface Ni of Ni/ZnO to form Ni3S2(Huntley, D. R. et al., “Desulfurization of Thiophenic Compounds by Ni(111): Adsorption and Reactions of Thiophene, 3-Methylthiophene, and 2,5-Dimethylthiophene,” J. Phys. Chem. 1996, 100, 19620-19627; Novochinskii, C. Song, et al., “Low-Temperature H2S Removal from Steam-Containing Gas Mixtures with ZnO for Fuel Cell Application. 1. ZnO Particles and Extrudates.”, Energy Fuels 18 (2004) 584; A. Ryzhikov et al. “Reactive adsorption of thiophene on Ni/ZnO: Role of hydrogen pretreatment and nature of the rate determining step,” Applied Catalysis B: Environmental 84 (2008) 766-772; L. Huang et al, “In situ XAS study on the mechanism of reactive adsorption desulfurization of oil product over Ni/ZnO,” Applied Catalysis B: Environmental 106 (2011) 26-38—each incorporated herein by reference in its entirety). Zinc oxide is also reported to be one of the most practical metal species for adsorptive desulfurization because of its large interaction with sulfur impurities and it has the highest equilibrium constant for sulfidation (I. Rosso, et al., “Zinc oxide sorbents for the removal of hydrogen sulfide from syngas,” Ind. Eng. Chem. Res. 42 (2003) 1688-1697—incorporated herein by reference in its entirety).
Ayala et al (R. E. Ayala, D. W. Marsh, Characterization and long-range reactivity of zinc ferrite in high-temperature desulfurization processes, Industrial and Engineering Chemistry Research 30 (1991) 55-60—incorporated herein by reference in its entirety) reported that zinc oxide with a very high equilibrium constant has high precision and shows stable and reliable performance in removing H2S.
The need for cleaner burning fuels has resulted in a continuing world-wide effort to reduce sulfur levels in hydrocarbon-containing fluids such as gasoline and diesel fuels. The reduction of sulfur in such hydrocarbon-containing fluids is considered to be a means for improving air quality because of the negative impact the sulfur has on the performance of sulfur-sensitive items such as automotive catalytic converters. The presence of oxides of sulfur in automotive engine exhaust inhibits and may irreversibly poison noble metal catalysts in the converter. Emissions from an inefficient or poisoned converter contain levels of non-combusted, non-methane hydrocarbons, oxides of nitrogen, and carbon monoxide. Such emissions are catalyzed by sunlight to form ground level ozone, more commonly referred to as smog.
Most of the sulfur in a hydrocarbon-containing fluid such as gasoline comes from thermally processed gasolines. Thermally processed gasolines such as, for example, thermally cracked gasoline, visbreaker gasoline, coker gasoline and catalytically cracked gasoline (hereinafter collectively referred to as “cracked-gasoline”) contains, in part, olefins, aromatics, sulfur, and sulfur-containing compounds.
Since most gasolines, such as for example automobile gasolines, racing gasolines, aviation gasolines, boat gasolines, and the like contain a blend of, at least in part, cracked-gasoline, reduction of sulfur in cracked-gasoline will inherently serve to reduce the sulfur levels in most gasolines such as, for example, automobile gasolines, racing gasolines, aviation gasolines, boat gasolines, and the like.
The public discussion about gasoline sulfur has not centered on whether or not sulfur levels should be reduced. A consensus has emerged that lower sulfur gasoline reduces automotive emissions and improves air quality. Thus, the real debate has focused on the required level of reduction, the geographical areas in need of lower sulfur gasoline, and the time frame for implementation.
As the concern over the impact of automotive air pollution continues, it is clear that further efforts to reduce the sulfur levels in automotive fuels will be required. While the current gasoline products contain about 330 parts per million (ppm), the U.S. Environmental Protection Agency recently issued regulations requiring the average sulfur content in gasoline to be less than 30 ppm average with an 80 ppm cap. By 2006, the standards will effectively require every blend of gasoline sold in the United States to meet the 30 ppm level.
Desulfurization preferably has a minimal effect on the olefin content of such fuels so as to maintain the octane number (both research and motor octane number). Such a process would be desirable since saturation of olefins greatly affects the octane number. Such adverse effect on olefin content is generally due to the severe condition normally employed, such as during hydrodesulfurization, to remove thiophenic compounds (such as, for example, thiophenes, benzothiophenes, alkyl thiophenes, alkylbenzothiophenes, alkyl dibenzothiophenes and the like) which are some of the most difficult sulfur-containing compounds to be removed from cracked-gasoline. In addition, there is a need to avoid a system wherein the conditions are such that the aromatic content of the cracked-gasoline is also lost through saturation. Thus, there is a need for a process wherein desulfurization is achieved and the octane number is maintained.
There is also a need to reduce the sulfur content in diesel fuels. In removing sulfur from diesel fuels by hydrodesulfurization, the cetane is improved but there is a large cost in hydrogen consumption. Such hydrogen is consumed by both hydrodesulfurization and aromatic hydrogenation reactions.
Conventional desulfurization requires a significant consumption of hydrogen and has poor economical performance process for the treatment of cracked gasolines and diesel fuels.
As a result of the lack of success in providing a successful and economically feasible process for the reduction of sulfur levels in cracked-gasolines and diesel fuels, it is apparent that there is still a need for a better process for the desulfurization of such hydrocarbon-containing fluids which has minimal effect on octane levels while achieving high levels of sulfur removal.
The present invention addresses the deficiencies of conventional materials by providing Alumina-NiO—ZnO and Alumina-ZnO composites for the desulfurization and removal of thiophene, benzothiophene and dibenzothiophene from model diesel fuel.
Traditionally, sorbent compositions used in processes for the removal of sulfur from hydrocarbon-containing fluids have been agglomerates utilized in fixed bed applications. Because of the various process advantages of fluidized beds, hydrocarbon-containing fluids are sometimes used in fluidized bed reactors. Fluidized bed reactors have advantages over fixed bed reactors such as better heat transfer and better pressure drop. Fluidized bed reactors generally use reactants that are particulates. The size of these particulates is generally in the range of about 1 micron to about 1000 microns. However, the reactants used generally do not have sufficient attrition resistance for all applications. Consequently, finding a sorbent with sufficient attrition resistance that removes sulfur from these hydrocarbon-containing fluids and that can be used in fluidized, transport, moving, or fixed bed reactors is desirable and would be of significant contribution to the art and to the economy.